1. Field of the Invention
The present invention generally relates to an end cap assembly for housing a solenoid adapted for use with a fuel injector and, more particularly, to a solenoid end cap assembly with a flat surface.
2. Background Description
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a valve control body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports and venting ports of the valve control body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid which is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In current fuel injector designs as shown in FIG. 1, a dowel ring assembly 101 is used to couple open and closed coil solenoids 100A and 100B to respective sides of a valve control body 102 of the fuel injector. The open and closed coil solenoids 100A and 100B include respective protruding coils 100A1 and 100B1. Both the ring dowel assembly 101 and the respective protruding coils 100A1 and 100B1 are set within a cut or milled portion 102A of the valve control body 102 (typically referred to as a “seat”). The cut portion 102A also provides a pathway (i.e., a magnetic circuit) for magnetic flux flowing between the open and closed coil solenoids 100A and 100B, the valve control body 102 and a spool 110 and back to the open and closed coil solenoids 100A and 100B.
In operation, a driver will first deliver a current or voltage to an open side of the open coil solenoid 100A. This current or voltage generates high temperatures about the open and closed solenoids which need to be dissipated by a heat sink. In any event, the magnetic force generated in the open coil solenoid will shift the spool 110 into the open position so as to align grooves or orifices 108 (hereinafter referred to as “grooves”) of the valve control body and the spool 110. The alignment of the grooves 108 permits working fluid to flow into an intensifier chamber from an inlet portion 104 of the valve control body via working ports 106. The high pressure working fluid then acts on an intensifier piston to compress fuel located within a high pressure plunger chamber. As the pressure in the high pressure plunger chamber increases, the fuel pressure will begin to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, a needle check valve will shift against a needle spring and open injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine.
To end the injection cycle, the driver will deliver a current or voltage to a closed side of the closed coil solenoid 100B (again generating high temperatures). The magnetic force generated in the closed coil solenoid will then shift the spool 110 into the closed or start position which, in turn, will close the working ports 106 of the valve control body. The working fluid pressure will then drop in the intensifier chamber and high-pressure chamber such that the needle spring will shift the needle to the closed position. The nozzle tip, at this time, will close the injection holes and end the fuel injection process. At this stage, the working fluid is then vented from the fuel injector via vent holes surrounding the valve control body.
This type of conventional assembly and especially the use of the dowel ring assembly presents many problems during the operation of the fuel injector, itself, as well as in the manufacturing process. First, in order to use the dowel ring assembly, a ring dowel seat must be milled into both the solenoid cap and the valve control body of the fuel injector. This is a complicated process which requires very tight manufacturing tolerances. However, it is very difficult, if not impossible, to provide the same exact diametrical clearances for each ring dowel seat from one fuel injector to the another fuel injector. It is only practical to provide tolerances within a certain range for each fuel injector, thereby resulting in certain built-in variances for each ring dowel seat. This, of course, results in the ring dowel assembly and hence the coil solenoids being seated on the valve control body differently for each injector (due to the different diametrical clearances). Due to these variances, the transmission of magnetic flux or conductivity will vary from fuel injector to fuel injector thereby producing different performance characteristics of the fuel injector; that is, the spool will shift at different rates. This is an undesirable effect which may contribute to an inefficiency of the engine operations.
The different diametrical clearances and the use of the ring dowel assembly in conventional systems also affect the thermal conductivity or transmission of heat between the parts of the fuel injector. For example, in use, the parts of the fuel injector are typically heated to temperatures within the outer limits of their tolerances. In using a ring dowel assembly, the seating of the solenoid coils and the solenoid cap, itself, may result in a space or gap between the valve control body and the solenoid coils. In this scenario, heat cannot be efficiently transmitted from the solenoid coils to the control valve body. In some types of engines, this may cause overheating of the solenoid coils, potentially damaging the solenoid coils or other parts of the fuel injector. If this happens, the solenoid coils must be replaced which adds to overall maintenance costs.
Lastly, in conventional systems, the overall cost of manufacturing the fuel injector remains high. By using the ring dowel assembly, separate precise and exacting milling processes have to be provided to the solenoid cap and the control valve body. Additionally, added pieces are required and, importantly, added assembly steps are required in order to assemble the fuel injector. These added steps include, amongst others, press fitting the ring dowel into the solenoid cap.
The present invention is directed to overcoming one or more of the problems as set forth above.